A friend of mine believes that people with disposable income look younger because they can choose to pay for cosmetic "help." People who have to struggle more in life for the necessities not only can't do that but the worry and stress they face daily shows up in their physical countenance.
Something I believe is that people with darker skin age better because their skin is more resilient and not so vulnerable to wrinkles and sun damage.
I do think that most folks will not accurately guess someone's age if asked because of fear of offending.
On the other hand, I am also quite open to hearing that 8-9 hours of sleep a night, a diet free of junk and preservatives, meticulous skin care habits, etc. are really what makes a difference for some people (so why don't I start doing those things for myself, haha)?